The present invention relates to steam irons in which steam is produced in a quasi-instantaneous manner. These appliances have a useful life that is limited by the build up of scale in the steam chamber.
Numerous devices for reducing the occurrence of scale in an iron have been proposed. One of the most successful physical-chemical systems diffuses a phosphorated product into water before the water is vaporized in order to impede crystallization of the scale in a hard form and to permit its removal by the steam flow. French patent FR 2 757 364 describes an embodiment of such a device where the diffusion of sodium hexametaphosphate (SHMP), which is highly soluble, is controlled by a silicone matrix placed in the water circuit. However, it has been noted that the scale that is formed tends to partially agglomerate under the action of the steam and detaches in the form of flakes that are friable but that are evacuated in bunches that stain the fabric being ironed.
The particles can be retained in the steam chamber by a metal screen as suggested in the German patent DE 3006783 or the Japanese patent 60160999. A screening can equally be produced in a manner disclosed in the French patent FR 2 696 197 where a grid intended to improve the vaporization has its edges raised in the form of bowl. However, the utilization of a screening grid alone eventually provokes blockages of the steam chamber by very hard scale, which cannot be evacuated.
The present invention has as an object a scale reducing device that will prolong the useful life of a steam iron while permitting regular evacuation of scale in a powder form powder that is invisible to the user and will not stain articles being ironed, while preventing obstruction of the chamber as well as of the steam vaporization channels, including the steam delivery holes in the iron soleplate.
The above and other objects are achieved, according to the invention, by a steam iron composed of: a metal heating body containing a chamber that has a steam generating zone; means defining a water flow path in communication with the chamber, the water flow path including a compartment containing a quantity of a scale reducing agent that is contacted by water flowing along the path before the water reaches the chamber, the scale reducing agent being obtained by cross-linking or hardening a silicone elastomer of an organosilicic system that is permeable to water vapor and having an active hydrophilic material and a polyorganosiloxane composition; and a screen made of a metal different from that of the heating body and disposed in proximity to the steam generating zone at a location to be traversed by steam generated in the steam generating zone.
The scale reducing agent could be fabricated in the manner disclosed in French patent FR 2 757 364.
Preferably, the active hydrophilic material is selected from among the metaphosphates of sodium or of potassium. It has been found that in the case of steam irons according to the present invention, no visible flakes exit through the steam delivery holes of the soleplate even when the screen has holes with a hydraulic diameter of the order of two millimeters. Surprisingly, scale does not accumulate in the steam chamber, or in the steam flow channels.
Preferably, the screen is fitted, or gripped, or clamped, tightly between two walls of the steam chamber of the pressing iron.
The process that permits the scale to be present in the form of a very fine powder that is not visible at the outlet of the iron is not clearly understood. Possibly, the friable flakes that detach from the steam generating zone are retained and rub against the screen, which breaks them into the very fine particles. Possibly, the scale that is deposited on or against the screen is broken up by thermal expansion and contraction of the screen. It is also possible that there is an unknown phenomenon resulting from the difference in electrical potential caused by the different characteristics of the metal making up the heating body and the different metal of the screen. This difference in electric potential could have an effect due to the good electric connection resulting from the tight gripping of the screen in the heating body.
Preferably, the screen is coated with a gold layer. This layer protects the screen and prevents it from rusting or corroding. It is also noted that the gold gives rise to a large electric potential difference with a heating body made of aluminum. According to another possibility, the screen can be made of stainless steal.
In either case, the screen is protected from oxidation phenomena and the appearance of a potential difference with a heating body of aluminum is promoted.
Also preferably, the screen is made of an expanded metal that is better able to break up the scale which comes to deposited on or against the screen.
Preferably, the scale reducing agent is contained in a tube and librates its active ingredients through at least one open end of the tube.
The silicone can be in form of matrix molded into the tube without requiring another mold. The active material is librated with a kinetic of the order of unity. This means that the active material is librated at a substantially rate, at least when the temperature of the matrix remains substantially constant. The active material is librated through a progressive front of cracks in the matrix, which coincides with the cross section of the tube so that the liberation of active material is thus perfectly controlled.
Preferably, the tube containing the scale reducing agent is placed in the water reservoir of the iron. The scale reducing agent can be present in a quantity sufficient to assure a good functioning of the system during the entire expected useful life of the iron, or can be renewable. Placement in the water reservoir is simplified when the matrix is molded within the tube.